A variety of filters and filter media are used to clarify water in swimming pools, water parks, hot tubs, and spas. Sand filters are common for swimming pools and municipal water treatment. Diatomaceous earth filters are also used in swimming pools and water parks. Cartridge filters utilize a synthetic fabric enclosed in a plastic cartridge. The different filter media remove different sized particles. Sand filters are capable of removing particles of 20-25 microns, while cartridge filters are typically capable of removing particles of 5-10 microns. Diatomaceous earth filters remove particles of 1-3 microns, but have to be replaced frequently. Currently, there is no efficient method that can remove submicron (<1 micron) particulates from swimming pools.
Chitosan is known for use as a pool water clarifier. Chitosan is sold under the designation SEA-KLEAR by Vanson Halosource, Inc. of Redmond Wash.
U.S. Pat. No. 5,543,056 to Murcott et al. describes a method for the treatment of drinking water that treats the water with chitosan as a primary coagulant, and bentonite as a coagulant aid. Bentonite is a fine-grained inorganic clay of the mineral montmorillonite. Clays are hydrated aluminosilicates of calcium, sodium, magnesium, and iron. Murcott et al. describes the use of chitosan and bentonite as a substitute for aluminum sulfate with or without polymer, for the removal of particulates, color, and turbidity. Murcott et al. uses chitosan and bentonite for the removal of particulates from 2 microns to greater than 50 microns, but does not describe the removal of submicron particulates. Clays are insoluble in water, and their insolubility can lead to clogged filters and sediment throughout the system. Therefore, clays are not used in pools, hot tubs, and spas.
Nichols, in Chitosan: Chemistry and Use In Water Clarification, National Spa and Pool Institute Chemistry Symposium (1997), describes the use of chitosan for the removal of nonpolar hydrocarbons, such as those present in skin creams, moisturizers, and suntan lotions. The removal of oils with chitosan is believed to be due to the ability of chitosan to form the halogenated derivative N-halochitosan. However, while Nichols describes the removal of some oils, Nichols does not describe the removal of submicron particulates that can be obtained with the addition of a second coagulant aid, following the addition of chitosan, as in the present invention.
Accordingly, there is a need for a method for removing submicron particulates that can take advantage of existing filtration technology such as sand, diatomaceous earth or synthetic cartridge filters to provide clear water for recreation.